Triple-shape properties of a thermoresponsive poly(ester urethane)

Thermo-mechanical investigations on a segmented poly(ester urethane) have shown that the material displays triple-shape functionality: gradual heating (-60 degrees C -> 23 degrees C -> 60 degrees C) of programmed specimens leads first to the transformation from shape (A) to shape (B) and later from shape (B) back to permanent shape (C). In the essential two-step programming process, the first deformation state (B) is stabilized by crystallized soft segments at T < T-c, the second one (A) through the polymer's glassy state at T < T-g. The transition temperatures, as analyzed for the permanent-shaped polymer via DSC, are T-g approximate to -49 degrees C and T-m(onset) approximate to 34 degrees C; the material crystallizes when cooled at T-c(onset) approximate to 4 degrees C. For the characterization of the material's cyclic thermo-mechanical triple-shape properties, maximum deformations of epsilon(m1) = 100% for shape (B) and epsilon(m2) = 130% for shape (A) were tested. In cycles N = 2-5 averaged shape fixing abilities of 74% (shape A, -60 degrees C), 109% (shape B, 23 degrees C) and shape recoverabilities of 103% (A -> B) and 96% (B -> C) could be detected. Values larger than 100% indicate the occurrence of plastic deformation during the second stretching.